Internally fed drum filter



Sept. 27, 1966 R. A. TAlT INTERNALLY FED DRUM FILTER 2 Sheets-Sheet 1Original Filed Feb. 4, 1965 Sept. 27, 1966 R. A. TAIT INTERNALLY FEDDRUM FILTER 2 Sheets-Sheet 2 Original Filed Feb. 4, 1963 United StatesPatent 3,275,150 INTERNALLY FED DRUM FILTER Ross A. Tait, Dorval,Quebec, Canada, assignor to Sherbrooke Machineries Limited, Montreal,Quebec, Canada, a corporation of Canada Continuation of application Ser.No. 256,173, Feb. 4, 1963. This application Oct. 12, 1965, Ser. No.500,478 11 Claims. (Cl. 210-327) This application is a continuation ofmy co-pending application, Serial No. 256,173, filed February 4, 1963,and now abandoned.

This invention relates to rotary drum filters and more particularly todeckers useful in the thickening of slurries such as those involved inthe manufacture of paper. Such apparatus generally comprises a drumrevolving in a vat or tank containing relatively thin paper pulp stock,fibers from the stock being deposited on the outside of the drum fromthe liquid-solid mixture to form a filter cake, mat or coating ofthickened slurry which is stripped or discharged from the drum as aportion of the drum rotates out of the stock in the vat. The excessfluid or filtrate is drained away and the discharged thickened slurry,mat or filter cake is processed further in the manufacture of paper.

Known equipment for the purposes above described is quite large andheavy and therefore needs a lot of space and requires considerable powerto drive.

One object of the present invention is to reduce the size of rotary drumfilter, particularly the length of the drum, so that for the samecapacity of equipment, economies may result in the required space,weight of equipment and power needed to drive the same.

A further object is to increase the efiiciency of gravity deckers, tothe end that greater recovery of fibers may be attained from stock of agiven consistency.

Another object is to provide such apparatus in which some operatingparts are cleaned by operation of the machine and others are readilyaccessible and easily may be cleaned during operation of the machine,thus reducing down time.

These objects are met generally by providing in the vat a double shelledrotary filter drum composed of a pairof radially spaced concentriccylinders of screen wire of filter mesh and providing an inlet pipe forslurry to be filtered, the inlet pipe discharging the slurry adjacent aclosed end ofthe inner screen cylinder. The slurry is thereby exposedfirst to the filter surface of the inner screen cylinder, filteringoutwardly, then to the filter surface of the outer cylinder, filteringinwardly to deposit a filter cake. The efliuent filtrate from bothscreens collects in the space between the cylinders, from which it isdischarged, the filter cake being collected from the outside surface ofthe outer cylinder. The inner filter screen in this arrangement acts asa pre-thickener of the slurry and occupies space not otherwise used inconventional deckers. There is no need for the usual inlet box.

Other objects, advantages and further details of that which is believedto be novel and included in this invention will be clear from thefollowing description and claims, taken with the accompanying drawingsin which is illustrated an example of decker embodying the presentinvention and incorporating the concentric filter cylinders withinternal feed and retroverted filtering discussed above.

In the drawings:

FIG. 1 is an elevational view of an exemplary drum filterlaccording tothis invention, as if seen from the intake end;

FIG. 2 is a longitudinal vertical sectional View through Patented Sept.27, 1966 ice the machine on a somewhat larger scale, as if taken on line2-2 of FIG. 1;

FIG. 3 is a transverse vertical sectional view on line 33 of FIG. 2,looking toward the filtrate discharge end of the machine;

FIG. 4 is a sectional view like the upper part of FIG. 3, showing amodification; and

FIG. 5 is a sectional view like part of FIG. 2 showing a furthermodification.

In carrying out the objects of this invention, in one embodiment thereofan outer housing and supporting framework 10 encloses and carries theother parts of the apparatus. Occupying most of the inside of thehousing is an inner stock tank or vat 12, shown here as of U-shape intransverse section, with ends closed by the end walls 14 and 16 of thehousing. At one end of the machine a central inlet for the liquid-solidmixture or slurry is provided in the form of an intake pipe 18 which isconnected to a suitable supply and extends from the wall 14 throughsubstantially the entire length of the tank in a manner and for thepurposes later described. The opposite end wall 16 is provided with anoutlet fitting 20 for discharge of the filtrate near the bottom of thetank or vat.

Thickening of the slurry introduced into the vat is accomplished by ahorizontally extending rotatably mounted and driven screen mesh filterdrum composed of two concentric radially spaced cylindrical filterwalls, an inner screen wall 22 and an outer screen wall 24. Thesecylinders are held in fixed concentric spaced relation one to the otherat one end by an imperforate annular radially extending end Wall 26closing the space between the inner and outer screen cylinders at theintake end of the machine, that end of the inner screen cylinder 22being open for reception of the intake pipe 18 and to permit slurrry topass from the inside to the outside of the drum. The other end of thefilter drum is provided with an imperforate central wall in the shape ofa disk 28 closing the end of the inner screen cylinder near the open endof the intake pipe 18. This disk is extended to the outer cylinder tosupport the cylinders concentrically and is provided with flow openings30 near its periphery leading from the annular space between thecylinders toward the outlet end wall 16. A suitable number of perforatedannular cylinder supporting walls 32 may be provided as found necessaryand desirable between the inner and outer screen cylinders to hold themproperly spaced and yet allow free flow of filtrate in the annularspace.

The double walled filter drum may be horizontally supported above thebottom of the vat and rotatably driven therein in any suitable fashion,for example by opposite outwardly extending trunnions (not shown) at thecenter of each end of the cylinder assembly. However, the cylindersupport and drive illustratedare of a character shown and claimed in thepatent application of Neil F. Putnam, U.S. Serial No. 3,855, filedJanuary 21, 1960 (Canadian Serial No. 814,589, filed January 11, 1961).In this type of mounting and drive the filter drum is provided withaxially outwardly extending cylindrical rims or end flanges 34 and 36,and the drum bangs and rides rotatably on pairs of bearing supportrollers 38, these rollers extending into engagement with the inside ofthe cylindrical rims from suitable support brackets 40 on .either end ofthe housing frame. Outer stabilizing rollers this end of the housingframework.

Inoperation, a thin slurry of pulp stock which itiS desired to thickenis fed into the machine through the intake pipe 18 and the motor 46 isstarted to drive the double cylinder in a rotary fashion. The thinslurry is discharged against the i-mperforate center of the disk 28 ofthe drum and is distributed evenly therefrom against the inner surfaceof the screen 22 inside this cylinder. Some of the Water or efiluentwill pass outwardly through the screen 22 so that as the slurry contactsthe rotating inner screen it will become somewhat thickened and thepartially thickened slurry will pass to the tank around the annularclosed end 26, being directed thereby and by the end wall 14 to thespace between the bottom and sides of the vat and the outside of theouter screen 24. The liquid filtrate which has passed through the screen22 will flow through the openings 30 and be directed to the outlet20,there being a sealing ring 48 on the end wall 16 slidably cooperatingwith the cylindrical flange 36 on the outside of the drum to preventmixture of the filtrate with unfiltered slurry from the vat 12. Furtherfiltnation and stripping are described later.

In :order to keep the filter surfaces on the inner screen 22 clean, acleaning shower head 50 may be provided next to the filter face of theinner screen near the top of the machine, extending along practicallythe entire length of the cylinder above the working level of the slurry,as shown. The shower head has spray openings 52 which direct cleaningwater upwardly against the wire 22 to scrub or clean it, water for thispurpose being provided under pressure from a suitable source through acleaning water inlet pipe 54, shown here as supported at one end by theslurry intake pipe 18. A post 56 may be provided to support the cleaningshower head at its far end.

FIG. 4 shows an alternative arrangement for cleaning the inner filterscreen, where it is not desired to dilute the slurry by the addition ofwash water. In this modification a series of spaced buckets or troughs51 are mounted in the annular space between the inner and outer screens,and as the drum rotates, each trough lifts some filtrate above the outersurface of the inner screen and dumps it against the inner screen whenabove the level of the stock in the machine. This gives a reverse flowof some of the filtered liquid through the inner screen, to dislodge andWash back fibers which may have collected on its inner filteringsurface. The shower head 50 may or-may not be used in this modification,as desired.

After the semi-thickened slurry passes around the, annular end wall 26and outside of the screen 24 as above described, the pre-thickenedslurry in the vat is directed against the rotating outer filter screen24. Filtrate passes inwardly through the outer cylinder, into theannular space between the filter cylinders, flows through the openings30 and is withdrawn through the outlet 20 along with filtrate from theinner cylinder. A coating or mat of thickened slurry or filter cake isconsequently deposited on the outside of the cylinder 24 and by rotationof the drum member it is carried out of the vat to a discharge devicefor stripping the filter cake or thickened pulp mat from the outside ofthe cylinder. As shown, this stripper may be a suitable couch dischargeroll 58 and doctor blade 60,.

or it may be a discharge roll of the character disclosed in US. patentapplication, Serial No. 772,928, filed November =10, 1958 by John P.Rich, and now US. Patent No. 3,032,201 (Canadian Serial No. 786,060,filed November 9, 1959). A stock slide or chute 62 may be arranged underthe discharge roll to direct the stripped filter cake away from themachine.

FIG. shows a further modification whereby the filtrate from the innerscreen maybe kept separate fnom the filtrate passing through the outerscreen. In this form of the invention an imperforate cylindricaldividing wall 23 is provided between the. inner screen wall 22 and theouter screen cylinder 24. Sets or rows of flow openings 29 and 31circularly arranged near the edge of disk 28 lead respectively from theannular space between inner screen 22 and wall 23 and from the annularspace hetween wall 23 and outer screen 24. Perforated annular supportingwalls 33 hold the screen cylinders and dividing wall in properly spacedrelation but allow free flow of the filtrates in the separate annularspaces provided by this construction. At the end of the drum, besidesend flange 36, another circular flange 37 is provided on the drum,located between and separating the circular row of holes 29. fromt-herow of holes 31.

In this form, instead of the single outlet fitting for mixed filtratesfrom inner and outer screens, an outlet pipe 20 is provided in the endwall 16 of the vat to draw off filtrate from the inner screen, and aseparate outlet pipe 21 for filtrate from the outer screen. The sealingring 48, as before, slidably cooperates with the flange '36, and in thiscase prevents mixture of the filtrate from the outer screenwithunfiltered slurry in the vat and directs filtrate to the outlet pipe21. An additional'annular sealing ring 49 is provided on the end Wallopposite the edge of the flange .37 and slidably cooperating therewith,to prevent mixture of the filtrate from the inner screen with the otherfiltrate and to direct the inner screen filtrate to the outlet pipe 20'.

The inner screen filtrate with this arrangement in most cases will beconsiderably more cloudy than the separate outer screen filtrate, whichmay be nearly clear. If the fiber content of the cloudy filtrate is highenough, it may be recirculated through the decker or through anothermachine to increase the total yield or efficiency .of the operation inremoving fiber from the slurry. Obviously either the shower head orreverse wash cleaning of the inner screen cylinder might be used withthe separate cloudy-clear filtrate discharge of FIG. 5, depending uponthe initial stock and the results desired.

If desired, the inner and outer screens may be of different gauge,taking advantage of the difference in consistency of the slurry insideand outside of the drum to improve the filtering action. A finer meshscreen on the inner cylinder may be preferred, to prevent undue fiberloss in the pre-thickening step.

As will be seen, the filtering of the slurry first outwardly against theinner filter screen and then in the otherdirection, inwardly against theouter filter screen from which the fully thickened slurry is collected,results in a machine which may be much shorter than machines ofcomparable output not using this inside-outside filter or retrovertedfilter arrangement. A given amount of filter area can be put in asmaller floor space than before. i

The anrangement-ofthis invention is advantageous not only because of thespace saved in equipment but also because it can increase the yield fromstock of a given consistency. The pre-thickening filtration through theinner cylinder proceeds with no difliculty, this screening operationbeing kept at an optimum rate because of the continuous removal of theusual hard skin of fibers from the screen by the shower or back-wash. Arelatively fine inner screen mesh may therefore be used without clog-Iging. Thereafter and! when the pre-thickened slurry reaches the outercylinder it is of a concentration that tends to form a comparativelyloose mat of fibers (rather than a hard skin), this mat itselfpermitting the. further filtration of slurry therethrough to buildup astill greater depth of cake than would have been possible with asinglescreen drum decker using stock of. the same initial consistency. T-heloose mat may be easily stripped from the outer 7 cylinder. 7

Because stock is present both inside and outside of the filter drum, amore balanced bouyancy is produced so that some reduction in weight andstrength of the parts safely may be made over usual requirements.

As the machine is operated, virtually all of the outer portions of thedrum assembly in contact with the stock are exposed for inspection andcleaning abovethe vat, and the inner portions are kept clean bythefcleaning water shower inside the inner cylinder 22 or by the reverseflow wash. There is but little obstruction to movement of slurry in themachine. Thus the apparatus may be used continuously for relatively longperiods and cleaning may be effected from time to time without haltingproduction. A product of uniform texture is therefore produced by thismachine.

Proposed operating levels for the slurry are shown in FIG. 3 of thedrawings, and it will be noted that the stock level in the innercylinder will be as high as possible and still allow the shower pipe toclean the wire of any mat formed on it. The level on the outer cylinderwill be very slightly less and of course, is governed by the maximumlevel in the inner cylinder with the difierence being the friction lossor head loss of the transfer of the stock from the inner to the outercylinder. These levels should be carried as high as possible to takeadvantage of the maximum amount of wire area for drainage purposes andalso to use the maximum amount of head to produce flow through bothsides of the cylinder.

As will be evident from the foregoing description, certain aspects ofthis invention are not limited to the particular details set forth as anexample, and it is contemplated that various and other modifications andapplications of the invention will occur'to those skilled in the art. Itis therefore intended that the appended claims shall cover suchmodifications and applications as do not depart from the true spirit andscope of the invention.

What is claimed as new and is desired to be secured by Letters Patent ofthe United States is:

Having thus described my invention, I claim:

1. In a decker of the type having a vat for containing pulp stock,

a drum rotatable within said vat adapted to collect filtered stockthereon as it rotates, and

means for rotating said drum within said vat,

said drum comprising an outer cylindrical filter screen,

an inner cylindrical filter screen within and concentric with said outerfilter screen, and

means supporting said inner and outer filter screens in-spaced relationto provide an annular open space therebetween,

first fluid carrying means communicating with a source of pulp stockexternal to said vat and extending within said inner filter screen forsupplying pulp stock to the inner surface thereof such that said pulpstock is partially thickened by said inner filter screen as said drumrotates, and

second fluid carrying means communicating the inner surface of saidinner filter screen with the outer surface of said outer filter screenfor conveying partially thickened pulp stock from the former and againstthe latter as said drum rotates such that filtered stock is collectedupon the outer surface of said outer filter screen.

2. In a decker of the type having a vat for containing pulp stock,

a drum rotatable within said vat adapted to collect filtered stockthereon as it rotates, and means forrotating said drum within said vat,said drum comprising an outer cylindrical filter screen, an innercylindrical filter screen within and concentric with said outer filterscreen, and means supporting said inner and outer filter screens inspaced relation to provide an annular open space therebetween, firstfluid carrying means communicating with'a source of pulp stock externalto said vat and extending within said inner filter screen for supplyingpulp stock to the inner surface thereof such that said pulp stock passeslongitudinally on and is partially thickened by said inner filter screenas filtrate passes outwardly therethrough to said annular open spaceduring the rotation of said drum, and

second fluid carrying means communicating the inner surface of saidinner filter screen with the outer surface of said outer filter screenfor conveying partially thickened pulp stock from the former andlongitudinally on the latter during the rotation of said drum such thatfiltered stock 1 is collected upon the outer surface of said outerfilter screen as filtrate passes inwardly through said outer filterscreen to. said annular open space.

3. A decker according to claim 2 wherein an imperforate cylindrical wallis disposed within said annular open space for maintaining the filtratepassing inwardly through said outer filter screen separate from thefiltrate passing outwardly through said inner filter screen.

4. In a decker of the type having a vat for containing pulp stock,

a drum rotatable within said vat adapted to collect filtered stockthereon as it rotates, and

means for rotating said drum within said vat,

said drum comprising an outer cylindrical filter screen,

an inner cylindrical filter screen Within and concentric with said outerfilter screen, and

means supporting said inner and outer filter screens in spaced relationto provide an annular open space therebetween,

first fluid carrying means communicating with a source of pulp stockexternal to said vat and extending within said inner filter screen forsupplying pulp stock adjacent one end of the inner circumference thereofsuch that said pulp stock is partially thickened by said inner filterscreen as filtrate passes outwardly therethrough to. said annular openspace during the rotation of said drum, and

second fluid carrying means communicating the other end of the innercircumference of said inner filter screen with the outer circumferenceof said outer filter screen for conveying partially thickened pulp stockfrom the former and against the latter during the rotation of said drumsuch that filtered stock is collected upon the outer circumference ofsaid outer filter screen as filtrate passes inwardly through said outerfilter screen to said annular open space.

5. Ina decker of the type having a vat for containing pulp stock,

a drum rotatable within said vat adapted to collect filtered stockthereon as it rotates, and

means for rotating said drum within said vat,

said drum comprising an outer cylindrical filter screen,

an inner cylindrical filter screen within and concentric withsaid outerfilter screen, and

means supporting said inner and outer filter screens in spaced relationto provide an annular open space therebetween,

first fluid carrying means communicating with a source of pulp stockexternal to said vat and extending within said inner filter screen forsupplying pulp stock adjacent one end of the inner circumference thereofsuch that said pulp stock is partially thickened by said inner filterscreen as filtrate passes outwardly therethrough to said annular Openspace during the rotation of said drum, and

second fluid carrying means communicating the other end of the innercircumference of said inner filter screen with the outer circumferenceof said outer filter screen for conveying partially thickened pulp stockfrom the former and against the latter during the rotation of said drumsuch that filtered stock is collected upon the outer circumference ofsaid outer filter 7 screen as filtrate passes inwardly through saidouter filter screen to said annular open space, and means for scrapingfiltered stock from the outer circumference of said outer filter screenduring the rotation of said drum. 6. In a decker of the type having avat for containing pulp stock,

a drum rotatable within said vat adapted to collect filtered stockthereon as it rotates, and means for rotating said drum within said vat,said drum comprising anouter cylindrical filter screen,

an inner cylindrical filter screen within and concentric with said outerfilter screen, said inner filter screen including a closed end, andmeans supporting said inner and outer filter screens in spaced relationto provide an annular open space therebetween, first fluid carryingmeans communicating with a source of pulp stock external to said vat andextending within. said inner filter screen for supplying pulp stock tothe inner circumference thereof adjacent said closed end thereof suchthat said pulp stock is partially thickened by said inner filter screenas it passes longitudinally thereon during the rotation of said drum,and second fiuid carrying means communicating the end of the innercircumference of said inner filter screen opposite to the closed endthereof with the outer circumference of said outer filter screen forconveying partially thickened pulp stock from the former andlongitudinally on the latter during the rotation of said drum such thatfiltered stock is collected upon the outer circumference of said outerfilter screen, and means for scraping filtered stock from the outercircumference of said outer filter screen during the rotation of saiddrum.

7. A decker according to claim 5 comprising in addition a shower headinside said inner filter screen, said shower head having spray openingstherein directed toward said inner filter screen and being operativelyconnected to a source of Water under pressure for supplying said waterto the inner circumference of said inner filter screen as said drumrotates.

8. In a rotary drum filter for thickening slurry having a vat containinga stock of slurry,

a filter drum mounted for rotation within said vat,

means for rotating said drum within said vat, and

means for stripping thickened slurry from the outside of said drum, thecombination of 7 said drum comprising an outer filter screen cylinderinwardly spaced from said ,vat, and

an inner filter screen cylinder concentric with and inwardly radiallyspaced from said outer filter screen cylinder to form an annular openspace between said inner and outer filter screen cylinders,

disk means closing one end of said inner filter screen cylinder,

a slurry inlet pipe operatively connected to a source of 8 slurryexternal to said vat and extending through the other end of said innerfilter screen cylinder towards said disk means for supplying slurryto-the inner circumference of said inner filter screen cylinder adjacentsaid disk means during rotation of said drum such that filtrate passesoutwardly into said annular space as said slurry passes longitudinallyover =the-inner circumference of ,saidinne'r, filter screen cylindertoward said other end thereof,

said other end of said inner filter screen cylinder being open'forconveying the thickened slurry from'said inner filter screen cylinderand across the outer circumference of said outer filter screen cylindersuch that thickened slurry is held by said outer filter screen cylinderas filtrate therefrom passes inwardly therethrough into said annularopen space,

an annular wall intermediate said inner filter screen cylinder and saidouter filter screen cylinder closing said annular open space atsaidother end of said inner filter screen cylinder, 2 said annular openspace at said one end of said inner filter screen cylinder being openfor permitting flow of filtrate from said annular open space, outletmeans in said vat communicating with said-an- -nular open space at saidone end of said inner filter screen cylinder for dischargingfiltratefrom said vat,

and means for sealing said outlet means from the thickened slurry-insaidvat.

9. A rotary drum filter according to claim 18 wherein means are providedfor washing said inner filter screen cylinder as it rotates, saidwashing means being operable above the level of stock in said vat.

10. A rotary drum filter according to claim 9 wherein said inner filterscreen cylinder washing means comprises a shower head located near thetop of said inner filter screen cylinder and above the level of stock inthe vat, said shower head being operatively connected to a source ofwash water'under, pressure.

11. A rotary drum filter according to claim *9 wherein said inner screenwashing means comprises a plurality of buckets mounted in said annularopen space between said inner and outer filter screen cylinders, each ofsaid buckets raising filtrate in said'annular open space above the levelof stock in the vatand dumping said filtrate back against the innerfilter screen cylinder assaid drum rotates.

References Cited by the Examiner 1 UNITED STATES ,PATENTS 870,138 111/1907 Stumpetal 210-393 1,212,978 1/1917 Malone 210+393 1,279,9499/1918 Waterman 210-403 1,504,020 8/1924 Brackett i. 210-236 1,636,7397/1927 Hertenbein 210333 X 2,454,134 11/1948 1 Burleson 210-342 X2,748,951 6/1956 Dubach 210403 3,025,213 3/1962 Copeland 210,.325 XREUBENFRIEDMAN, Primary Examiner. 'J. DE CESARE, Assistant Examiner,

1. IN A DECKER OF THE TYPE HAVING A VAT FOR CONTAINING PULP STOCK, A DRUM ROTATABLE WITHIN SAID VAT ADAPTED TO COLLECT FILTERED STOCK THEREON AS IT ROTATES, AND MEANS FOR ROTATING SAID DRUM WITHIN SAID VAT, SAID DRUM COMPRISING AN OUTER CYLINDRICAL FILTER SCREEN, AN INNER CYLINDRICAL FILTER SCREEN WITHIN AND CONCENTRIC WITH SAID OUTER FILTER SCREEN, AND MEANS SUPPORING SAID INNERR AND OUTER FILTER SCREENS IN SPACED RELATION TO PROVIDE AN ANNULAR OPEN SPACE THEREBETWEEN, FIRST FLUID CARRYING MEANS COMMUNICATING WITH A SOURCE OF PULP STOCK EXTERNAL TO SAID VAT AND EXTENDING WITHIN SAID INNER FILTER SCREEN FOR SUPPLYING PULP STOCK TO THE INNER SURFACE THEREOF SUCH THAT SAID PULP STOCK IS PARTIALLY THICKENED BY SAID INNER FILTER SCREEN AS SAID DRUM ROTATES, AND SECOND FLUID CARRYING MEANS COMMUNICATING THE INNER SURFACE OF SAID INNER FILTER SCREEN WITH THE OUTER SURFACE OF SAID OUTER FILTER SCREEN FOR CONVEYING PARTIALLY THICKENED PULP STOCK FROM THE FORMER AND AGAINST THE LATTER AS SAID DRUM ROTATES SUCH THAT FILTERED STOCK IS COLLECTED UPON THE OUTER SURFACE OF SAID OUTER FILTER SCREEN. 